Beyond the horizon

"one of the most important-ever breakthroughs in astronomy"…

Beyond the horizon

At High School in the Netherlands, Marielle van Veggel just “wanted to do something interesting” in her career, maybe something connected with Space. But even though being involved in “one of the most important-ever breakthroughs in astronomy” may look like mission accomplished, she’s now more interested in what will happen next. One of the biggest and most complex scientific experiments in history has finally managed to detect gravitational waves and observe a collision between two black holes – but what lies beyond the horizon? If the research team can develop much more sensitive detectors, what will they tell us in future?

For van Veggel, working on Advanced LIGO (the Laser Interferometer Gravitational-wave Observatory) has already delivered the result the researchers were hoping to find, and future detectors will be much more powerful systems, but she and other scientists have seen that some of their technologies can also be applied to other projects, including launching a gravitational-wave observatory into Space. This ambitious project, called LISA, is a major development sponsored by the European Space Agency with strong contributions from many countries, including scientists from the IGR and other research establishments in the UK (for more details, please see below).

Before she was recruited by the University of Glasgow ten years ago, van Veggel worked on a project called GAIA (please see sidebar). A graduate of the University of Eindhoven in the Netherlands, her experience in this ground-breaking project not only introduced her to the level of teamwork required for such experiments, but also involved interaction with private contractors, using the latest materials science to make the design for the spacecraft more lightweight and stable. Encouraged to accept a position in Glasgow by Professor Jim Hough, who had been one of the external examiners for her PhD Thesis, she “exported” her specialist knowledge to Scotland, helping to develop the silica mirror suspensions, and also developing a new kind of bonding technology which helps to cut noise and vibrations by simplifying how the different parts are connected.

As a member of the Glasgow research team, van Veggel loves to push on every front to develop the technology used in the mirror suspensions, working side by side with data analysts as well as other materials scientists, mechanical engineers and physicists to reduce noise to a minimum and create the “unbelievably accurate” system now operating in Advanced LIGO, while designing future versions which may not be switched on for decades. Van Veggel is comfortable working on such long-term projects – LIGO has only provided a hint of what later detectors may see, and other long-term projects, such as LISA (please see sidebar), will not even go into orbit for another 20 years.

The international dimension

The LIGO Scientific Collaboration (LSC) involves more than one thousand people, and van Veggel loves to feel part of such a large team, with scientists from different countries working on projects in Europe and the US as well as Japan, sharing data and exchanging new ideas. “Some friendly competition is a good thing,” says van Veggel, “but it’s also important to be open-minded, because we are working towards the same ultimate goal.”

Researchers in different countries have also taken slightly different approaches to the mirror suspensions, to improve sensitivity. For example, the configuration in Italy’s Virgo detector uses silica fibres developed in Glasgow, but connects the fibres differently to the mirror and suspension system above, using an inverted pendulum suspension – Advanced LIGO features a quadruple pendulum suspension, connecting four masses (the bottom one being the mirror) in a vertical chain before connecting to a vibration isolation system.

Van Veggel’s major contribution to the mirror suspensions developed in Glasgow is the bonding solution for the mirrors and silica fibres, to enable a low-noise and seamless connection for the “ears” on the sides of the mirrors. As well as installing the mirror suspensions in Washington State, van Veggel also helps to train the team.

According to van Veggel, the detectors of the future will be very different devices, using mirrors and fibres made of silicon or sapphire and including innovative cryogenic systems now being pioneered by KAGRA in Japan (the Kamioka Gravitational-Wave Detector), which will operate at sub-zero temperatures. Using “precious stones” may seem an unlikely solution, but van Veggel says that crystalline materials offer several advantages because they perform better at very low temperatures, helping the detector operate “with less noise disturbance.” Van Veggel has been involved in an exchange programme, working with KAGRA, providing advice on the bonding technology, and also works closely with scientists in the US who are investigating the possibility of Cosmic Explorer (a successor to LIGO) – a new detector with much longer arms and much bigger mirrors, weighing four times as much as the current design. Unlike the Japanese approach, however, this would operate at room temperature, thus “sticking to our trusted fused silica.”

The Einstein Telescope in Europe is another ambitious design, and van Veggel has been working on the project since 2010, when the new design for Advanced LIGO was already completed. “We move on very quickly from project to project,” says van Veggel. The new design will be ten times more sensitive than Advanced LIGO, according to van Veggel, and reveal 1,000 times more sources.

“It takes many years to design and construct a detector, and we were very fortunate to witness the detection,” says van Veggel. “But Jim Hough has been waiting even longer!”

So what will be van Veggel’s next career step? Apart from “tinkering” with new designs, to get another glimpse of gravitational waves and understand more about black holes and neutron stars crashing together in galaxies far, far away, she is already working on new applications and spin-offs – including new designs for laser crystal assemblies which utilise the same kind of bonding technologies as those planned for use in future crystalline mirror suspensions, designed to operate at very low temperatures.

But whatever van Veggel may do and wherever she goes, you can be sure it will be “something interesting,” whether she is tinkering in Scotland or Japan, or her mind is on higher things out there in Space.

GAIA

GAIA is a Space observatory (launched in December 2013) designed by the European Space Agency (ESA) to catalogue approximately one billion astronomical objects, including stars and planets, comets, asteroids and quasars – to create a precise three-dimensional map of astronomical objects and track their motion through Space. The “stellar census” is also expected to detect “thousands to tens of thousands” of Jupiter-sized exoplanets beyond the Solar System, 500,000 quasars and tens of thousands of new asteroids and comets within the Solar System, and help us understand the origin and evolution of the Milky Way. It will also analyse the physical properties of the stars, including luminosity, temperature, gravity and composition, to provide the basic data we need to answer a wide range of questions about the origin, structure, and history of our galaxy.

LISA

The Laser Interferometer Space Antenna (LISA), is a European Space Agency mission designed to detect and accurately measure gravitational waves (tiny ripples in the fabric of space-time) from astronomical sources, using laser interferometry. The concept is to have three satellites orbiting Earth, arranged in an equilateral triangle 2.5 million kilometres apart, then continuously measure the distance between them to detect a passing gravitational wave – gravitational waves alternately squeeze and stretch objects by a tiny amount, as they travel unhindered through matter and space. The mission was formally selected by the European Space Agency in June 2017 and is currently scheduled to launch in 2034. The Institute for Gravitational Research in Glasgow (IGR) designed and built the optical bench system for a prototype demonstrator satellite for LISA – LISA Pathfinder – in a project directed by Dr Harry Ward. LISA Pathfinder was launched in December 2015 and its performance has been judged to be outstanding, persuading the community and funding agencies that the main LISA project should be pushed forward with all possible speed.

Biographies

Dr Marielle van Veggel is a Royal Society Dorothy Hodgkin Research Fellow in the Institute for Gravitational Research (IGR) in the University of Glasgow. She has played a key role in developing and applying the bonding techniques used to attach the silica fibres to the silica test masses (mirrors) employed in the Advanced LIGO design – techniques which have significant potential for wider industrial application. In 2016, she shared the Special Breakthrough Prize in Fundamental Physics with the rest of the LIGO team, as well as other international prizes. Her work directly contributed to the Glasgow Herald Research “project of the year” award won by the team based in Scotland.

Dr Harry Ward, a Fellow of the Institute of Physics, leads the research towards the Space-borne gravitational-wave detector LISA in the IGR in Glasgow. Following earlier work towards the design and operation of both GEO600 and LIGO, he more recently directed the Glasgow team who designed and built the optical bench for LISA Pathfinder, a demonstration satellite to test the fundamental concepts behind the interferometry and control for the proposed LISA mission. Pathfinder, launched in December 2015, was highly successful and has provided a high level of confidence that the full LISA mission should be flown by ESA around 2034. For his work with the LISA Pathfinder team, Ward received a 2016 Sir Arthur Clarke Award.